Heating, cooling, and ventilation have become ubiquitous around the world. Heating is critical in winter months where temperatures fall well below freezing in many inhabited areas. Similarly, cooling makes hot regions such as the American southwest more livable in terms of temperatures. Around the world, a massive amount of energy is used each year to provide heating and cooling. The energy expended on heating and cooling is costly and leads to a choice between high energy bills or uncomfortable temperatures for consumers.
Inefficiencies in heating and cooling systems drive up energy costs significantly while providing little or no benefit in most cases. For example, many industrial processes produce waste heat as a byproduct. Generally, little or no useful work is accomplished with the waste heat. Thermodynamic cycles, such as absorption cooling, can provide environmental cooling even from low grade heat sources. However, absorption cooling technology suffers from inefficiency.
Energy costs are dependent on many factors, including the type of energy source and time of day. For grid power, the cost of electricity fluctuates heavily from peak hours to off-peak hours. For example, in some instances off-peak electricity can be less expensive than natural gas, while peak electricity is more expensive than the gas. Some energy sources are only available during certain times of day, such as solar energy. Thus, the bottom line efficiency in terms of heating or cooling per dollar spent fluctuates with relevant energy prices applicable to the heating or cooling source.
Motor driven heating and cooling units generally give off a large portion of the energy expended driving the motor as exhaust heat. The lost energy in exhaust heat increases the inefficiency of the heating and cooling unit. Additionally, electrical heating and cooling devices require the conversion of one form of energy into electricity and then back to thermal energy for heating and cooling. The inefficiency of converting energy reduces the efficiency of the electrical heating and cooling devices as a whole.
Heat sources are not always consistent in terms of temperature and availability. The temperatures of various heat sources expelled from industrial processes can fluctuate between hot and cold. When capturing heat from low grade heat sources, inconsistent temperatures can present obstacles to using the heat effectively. The availability of the waste heat may also be intermittent as the underlying process generating the heat produces either less heat or no heat at all. Similarly, solar energy is only generated during daylight hours. A heating and cooling system attempting to use heat as an energy source cannot stop and start intermittently as the availability and temperature of the heat fluctuates.